Back from a 3-day marathon at Laggy's place (during which we went from...early Chapter 4 to late Chapter 4; weird that).
Evaluation of Math Skills:
* [Math Skill] now has the following spells (and only these) available:
White Magic ... Cure, Cure 2,
Used rarely. We have lots of 80 faith people, which means this healing 300 HP without the Pray Faith status...did happen (which is damn good healing).
Reraise,
Trashes certain zodiacs (Zalera, Queklain, and Hashy I guess) just because all enemies are immune to reraise. Has some arguments for being the best overall revival in the game, but...at the same time I've set white magic on an LFT Mathskiller just so that we would have normal revival if someone died unexpectedly...and always had someone with regular revival in the party either way.
Regen, Protect, Shell, Wall,
Trashy as mathskills; were used in precisely one fight (Elibdibs to help learn Zodiac). The main issue is that the most defensive mathskills tend to be "status the enemy". If there was, say, a deep dungeon fight with lots of 3-faith enemies I might care about these (hint hint).
Esuna
Good, if for no other reason than there's a tendency to status your own party....
Black Magic ... Fire, Ice, Bolt,
Was averaging...150 damage by the end of the deep dungeon against average faith? (312 if you faith both sides). (This after the multiplier nerf, mind). Yeah, we've been over this one before: it's a lot of damage for an infinite range area move that your party can absorb. But...getting no abilities from Black Magic would be silly. Having no abilities based on MA would be silly (because then the only stat you care about is speed, so all mathskillers go Ninja, which is meh). Granted, there's still Cure 2 (which can be combined with Zombie for damage...and then you can block Zombie on your own party with 108 gems so you get the same heal&damage effect so...yeah).
Poison
Tried to make it work; in theory it has uses over demi, sometimes. In practice, enemies kept freaking healing it.
Time Magic ... Haste,
Definitely used, although we have actual Time Mages, so they typically handled it.
Slow,
Obviously pretty good debilitation status. Probably should have used it more in retrospect (CT5Slow followed by the Time Mage using Haste2 on us sounds like a good combo). Though it certainly saw a bit of use.
Don't Move,
Used occasionally, though not really abused to its full potential; we don't particularly have the party for it (no Dancer or anything like that).
Float, Reflect,
Were never used. Funny, I've definitely used CT5Reflect in regular FFT. (Well...Satan FFT; it has it's own rules).
Demi
The best damage when MA is low; used a fair bit as a Calc. Also often a good way to damage your own party members without killing them (since we tended to have much higher faith and much lower HP than the enemies).
Yin-Yang Magic ... Blind,
Learned it; don't think I ever used it, though. Although...if this party had any real evade then it would become the Black Chocobo counter that I couldn't find in the mathskill skillset.
Pray Faith,
Used nearly every fight--we basically had a party built around abusing it, though (three mages and an elemental gun user). Again I'm thinking back to Don't Move, and if it's not a problem then Pray Faith probably isn't either (also a build-around move).
Doubt Faith,
Used very rarely; enemies are usually better silenced or berserked; I believe I have used it defencively when someone walked into Meteor range.
Zombie,
Not sure I ever used it.
Silence Song,
Situational; fairly easy to cure thanks to cheap Echo Grass; blocked fairly often due to Golden Hairpin throughout most of Chapter 4. No effect on most enemies. Still useful when it works.
Blind Rage,
This is the surprise one that I wasn't expecting to be good, and I didn't even think of it all that often until after I got back, but I'm now thinking is one of the stronger abilities in the skillset. Enemy have a nasty skillset? Disable it. Examples include...
Jump w/ high level jumps
Elemental w/ Carve Model
Punch Art w/ Earth Slash
Item w/ Phoenix Down or status curing
Draw Out w/ Kikuichimoji
Math Skill w/ almost anything (hey, we saw it in three battles)
Choco Meteor
Triple Thunder
M-Barrier and Lifebreak (yeah, that guy).
It's also unusually hard to heal (Item can't do it; Choco Esuna can't do it) and almost never blocked (the only equipment that does is Magic Ring...which incidentally also blocks Silence anyway). Has the added bonus of disabling reaction abilities (along with Confusion Song...though doesn't wear off after the first hit like Confusion Song does).
(Side note: Berserk for disabling reactions strikes me as probably relevant against Behemoths, which have Damage Split, take several attacks to go down, and have a physical that OHKOs you even without Berserk plus some monster skills you'd rather never see).
Now, granted, I'm not that worried about it being overpowered. The two most common enemies are Knights and Archers, which just happen to be two units you really don't want to Berserk.
Confusion Song,
The all-around disabling status, more or less. (Well...it can compete with Slow). Cancels all charged enemy abilities. always good to use on an enemy, though not always the best. doesn't hurt too much when used on an ally. Disables all enemy evade and reaction abilities.
Dispel Magic
Used rarely; primarily for wiping out Reraise on enemies...although almost anytime you come across an enemy with Reraise you probably should take the time to Dispel Magic them, as I discovered. As for other positive statuses, Haste is better-countered with Slow, and Shell/Protect...if you're using a turn to help kill an enemy, getting rid of shell/protect is probably not as valueable as Demiing the enemy/Pray Faithing the enemy, or in some cases Don't Moveing/Confusing the enemy.